Interventional procedures, such as are applied, for example, in radiology, are today already playing an important part in the diagnosis and therapy of many illnesses. By way of example, certain instruments are used, such as needles, to reach a specific point in the body or inside an organ from the outside through the skin (percutaneous). This relates for instance to punctures, biopsies, ablations, or brachytherapies, or fixations, such as screws, are put in place.
Based on further technical developments of the imaging systems, the techniques referred to as modalities, such as, for example, computed tomography, magnetic resonance tomography, or angiography, are capable of identifying inflammatory or tumorous changes at increasingly early stages. In order to impose as little burden on the patient as possible, minimal-invasive interventions are increasingly frequently being carried out at very early stages, when the changes have still only extended over a comparatively small space. In addition, increasingly finer instruments are being developed for punctures, catheterization, and scanning of the organ systems. In order for increasingly smaller target regions in the body to be accessible with increasingly finer instruments, increasingly more precise and accurate navigation methods are also required.
Due to the fact that the physician cannot directly see the instrument in the body of the patient, he is reliant on the support of imaging methods. Ideally, the physician will have available, prior to the intervention, a 3D data record of a modality (e.g. magnetic resonance tomograph, computed tomograph, angiography device) in which he can identify the target region and, based on the physiology, can plan the ideal way to reach it, and therefore the entry point for the instrument. In a simpler variant, the target region will be identified during the intervention, for example by means of a C-arm X-ray device, which can produce CT images, and further planning can be undertaken on the basis of the combined information from 2D and 3D data from the X-ray device. With this planning, the entry point on the body and the orientation of the interventions instrument, e.g. a needle, can be determined.
In general, a planning of the entry route of the instrument is carried out by the physician by means of a planning system, i.e. by virtual means with the aid of software suited thereto, and then transferred manually to the interventional instrument, which can be carried out with robot support.
The intervention plan can then be passed to a navigation system, which is registered with the 3D data record. The navigation system can control or support the alignment of the instrument by means of a variety of different manual or automatic methods. The advance of the instrument can be monitored in this situation radioscopically, i.e. in real time under X-ray radioscopy or by ultrasound. As an alternative, the pre-interventional 3D data record can be co-registered with the C-arm data record, and the information then used for the navigation.
Problems arise, for example, in situations involving adipose or heavily-built patients. Due to the technical realization of the C-arm X-ray device, only a limited volume of the body can be reconstructed. It may therefore occur, for example, that the surface of the body is not included in the 3D data record. With virtual planning, in this situation the physician cannot identify where the insertion point is located, and whether the planned access path may possibly be unsuitable for the intervention due to the superimposition of bones or ribs.
At the present time, for example, a fine-needle biopsy or a thermoablation of a focal point in the liver by a percutaneous route is carried out in most cases under CT-monitoring. In this situation, the physician carrying out the procedure makes use for his access planning of a combination of the CT sectional image, of markers applied to the surface of the skin of the patient, and of the orientation assistance provided by a laser reticule located on the CT gantry.
With this procedure, the actual puncture and the advance of the instrument are carried out essentially manually by the physician. Depending on his degree of experience, a multiple puncture will be necessary in this situation. This procedure, as well as involving unpleasant effects for the patient, also incurs an increased risk of complications, such as bleeding, organ injury, or hematoma. In addition to this, the precision of the puncture is restricted with this procedure, in particular with very small target regions.
In order to achieve more precisely targeted instrument guidance, a number of other different navigation aids are used, such as, for example, optical or electromagnetic location systems, or the use of a stereotactical frame, the position of which in space is known, and which exhibits an apparatus for instrument guidance. This procedure, however, is elaborate. As well as this, the distal end of the instrument, away from the patient, can be monitored by location systems. This means, however, that account cannot be taken of deformations of the instrument, e.g. of the tip of a needle, caused due to resistances in the body, and which under certain circumstances may lead to a deviation from the puncture path.
From the publication DE 10 2007 045 075 A1 an interventional navigation system is known, which exhibits a multi-axle robot arm for guiding an instrument secured to it. The robot arm exhibits a yield movement control system, by means of which the robot arm can give way in a monitored manner in response to external force effects, such as manual forces. As a result, the instrument can be positioned by the user manually and at the same time be held automatically by the navigation system in the desired orientation and position or, respectively, on the desired path. To achieve this, 3D data from the patient, the robot arm, and the intra-operative imaging device must be mutually registered.
The prior art represented in DE 10 2007 045 075 A1 makes it possible, for example, for the physician conducting a biopsy to pre-position a robotic needle guide manually, and the robot then takes charge of the final placement and alignment of the needle. To achieve this, mention is made of an array of methods for position recognition, all of which are based on external location techniques (optical, electromagnetic navigation) or on a fixed mechanical registration. With mechanical registration, the intention is that the robot should be mounted in a fixed position relative to the C-arm system.
If such a system is to be used in the surgical environment, however, a number of limitations may arise. With procedures for the fixation of the vertebral column, for example, a plurality of screws are introduced into different vertebral bodies. With a fixed mechanical registering of the instrument holder, regular and elaborate calibration is necessary in order to guarantee exact positioning when introducing the screws. This calibration is prone to faults, since random mechanical effects on the instrument holder in the operating theater cannot be excluded. Because correct and exact calibration is necessary for the precise application of the screws, the calibration must accordingly be frequently repeated. This is time-consuming and not practicable in the operation environment.
If, instead of this, an additional external location technique (optical, electromagnetic navigation) is used, the patient must first be registered with the operation plan (e.g. planned screw position). The patient and the instrument holder must then be registered with the location technique. The large number of registration steps is elaborate and time-consuming. In addition to this, additional location systems must be omitted, since their hardware is often in the way, as well as prone to faults.